The present invention relates generally to methods for producing fatty acid esters by the reaction of an ester and another organic compound with the exchange of alkoxy or acyl groups. More particularly, the present invention relates to methods for the transesterification of triglycerides such as vegetable oils or animal fats to produce fatty acid esters that may be used in the economical production of biodiesel.
Biodiesel is the common name for mono alkyl esters of long chain fatty acids derived from vegetable oils or animal fats. Biodiesel is a promising alternative fuel source suitable as a diesel fuel or diesel fuel lubricity additive because it is biodegradable, non-toxic, and has low emission profiles as compared to conventional fuels. However, high raw material and processing costs have limited the widespread use of biodiesel.
The most common method of producing biodiesel is the base-catalyzed transesterification (or alcoholysis) of triglycerides such as vegetable oils and animal fats. The transesterification reaction involves reacting the triglyceride with an alcohol to form fatty acid esters and glycerol. The reaction is sequential wherein the triglycerides are converted to diglycerides, monoglycerides and then to glycerol with a mole of ester liberated at each step. Transesterification of oils and fats also has been described in connection with the production of detergents, cosmetics, and lubricating agents.
Historically, triglycerides in fats and oils have been methylated or otherwise esterified in a two-step process using an acidic catalyst, such as is described in the U.S. Pat. No. 4,695,411 to Stern et al., U.S. Pat. No. 4,698,186 to Jeromin et al., and U.S. Pat. No. 4,164,506 to Kawahara et al. Transesterification processes employing alkaline catalysts, such as U.S. Pat. No. 5,525,126 to Basu et al., U.S. Pat. No. 5,908,946 to Stern et al., and U.S. Pat. No. 6,538,146 to Turck, have been known in the art, as well.
Application of prior art has, with some frequency, resulted in the production of lower alkyl ester products that do not meet applicable national or international quality specifications for B100 biodiesel (a pure biodiesel product not blended with petroleum diesel). Frequently, these quality problems, such as gelling, can be attributed to an insufficient degree of conversion of process feedstocks, insufficient yield of alkyl ester products, and incomplete separation of reaction products. The invention subsequently described results in improved degrees of conversion and yield, and efficiencies in product separation, including such that the resulting B100 product meets or exceeds applicable specifications, most notably ASTM D6751 and the more rigorous EN 14214.